U.S. Pat. No. 4,553,962 A discloses an automatic syringe comprising a C-shaped clip releasably fitted to a housing. DE 102007031714 A1 shows a single-use injector.
One problem of a drug delivery device is that the user cannot see if the device is in a primed or un-primed condition. That means that the user does not know if he has primed the device before or not. So the user cannot see if he has to perform a priming step before he can use the device in a correct way.
For example, users who are unfamiliar with the drug delivery device may forget to prime the device before dispensing the first dose. In case that the drug delivery device is, for example, an injector, and if the user does not prime the device before the first use, the user may inject an incorrect volume of drug during the first injection. This could happen because in an un-primed condition there may be gaps between the different parts of the device which are taken up when the device is operated for the first time to set or dispense the drug. These gaps may be a consequence of the manufacturing or assembling tolerances. These gaps may be considerable before the first operation but may be less considerable or not present at all afterwards.
Priming the device means that these gaps are reduced or removed by performing a priming step. After having performed the priming step, the device is in a primed condition so that the user can dispense the intended dose accurately.